1. Field of Invention
This invention generally relates to detecting and maintaining good image registration in color image processing. More particularly, this invention relates to methods and systems in which image registration between color separation images of a full color image is monitored and adjusted during a print run.
2. Description of Related Art
Electrophotography, a method of copying or printing documents, is performed by exposing an image representation of a desired original image onto a substantially uniformly charged photoreceptor, such as a belt. In response to that image representation, the photoreceptor discharges to create a latent image of the desired original image on the photoreceptor""s surface. Developing material, or toner, is then deposited onto the latent image to form a developed image. The developed image is then transferred to a final substrate, such as paper. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the production of another image.
Color images may be produced by repeating the above process once for each differently colored toner that is used to make a composite color image. For example, in one color imaging process, referred to herein as the Recharge, Expose, and Develop, Image On Image (REaD IOI) process, a charged photoreceptor surface is exposed to an image which represents a first color. The resulting electrostatic latent image is then developed with a first colored toner to form a first color separation image. The charge, expose and develop process is repeated, for example, for a second colored toner, then for a third colored toner, and finally for a fourth colored toner to form second, third and fourth color separation images. The various differently-colored color separation images are placed in superimposed registration with the first developed color separation image so that a desired composite color image results. The composite color image is then transferred and fused onto an image recording substrate or medium.
Registration offsets in a developed image are undesirable because, if the developed image is transferred to a final substrate without adjusting for the registration offsets, the final transferred image will include the registration offsets. That is, each different color separation image will be slightly misregistered, or offset, relative to the other color separation images and/or the receiving substrate. These registration offsets, even if only a few mils or tens of microns, are well within the visual acuity of the human eye. Since the human eye can sense these misregistrations, the quality of the resulting image suffers greatly even for small registration offsets.
This invention provides color imaging methods and systems where each color separation image is to be registered in a composite manner.
This invention provides systems and methods that improve the registration between the color separation images.
This invention separately provides systems and methods that control the output of the image data for one or more of the color separation images to remove or reduce registration offsets.
This invention separately provides an image-on-image registration controller for an image forming device that controls the output of the image data for one or more of the color separation images to reduce or eliminate image registration offsets.
This invention separately provides first control systems and methods that control the output of the image data based on higher frequency but transitory offset results from dynamic skewing of the image forming device.
This invention separately provides for second control systems and methods that control the output of the image data based on lower frequency offsets resulting from thermal and other slower variations in the image forming device.
This invention separately provides control systems and methods that directly measure the positions of the color separation images on the image forming device.
This invention further provides marks-on-belt sensors to directly measure the positions of the color separation images on the image forming device.
This invention separately provides systems and methods that switch between first control systems and methods and second control systems and methods.
The systems and methods of this invention combine two separate feedback techniques so that the image registration can be monitored and adjusted without going off-line for a set-up procedure. In one aspect of the systems and methods of this invention, a dynamic skew control feedback loop in which the edge position of the photoreceptor belt is monitored and adjusted to infer lateral registration is combined with a direct image registration feedback loop in which the relative image registration is directly monitored and adjusted.
The systems and methods of this invention eliminate many off-line set-up procedures and increase the image quality by constantly adjusting for registration offsets.
In accordance with the systems and methods of this invention, problems in registration, such as misalignment, are reduced or eliminated without going off-line.
In another aspect of the systems and methods of the invention, image data is adjusted based on determined image registration offsets. In yet another aspect of the systems and methods of this invention, the image processing device outputs an image based on image control data adjusted based on determined image registration offsets.
The systems and methods of this invention provide an image processing device that, as the image registration changes, determines and applies the necessary adjustments to the image control data to keep the different color separation images registered throughout the print run.
These and other features and advantages of the systems and methods of this invention are described in or are apparent from the following detailed description of the preferred embodiments.